1. Field of the Invention
This invention relates to wireless communications; and more particularly to antenna arrays for integration with access points, wireless mobile devices, and communication systems, to service a multitude of functions including phased arrays, multiple input multiple output (MIMO), receive diversity, and direction finding.
2. Related Art
There is a current need for improved connectivity at cellular and data transmission bands for mobile wireless devices and access points to accommodate the increasing demand for data rates for mobile wireless systems. Improved antenna performance, such as increased efficiency, will translate into increased data rates. Another effective method of improving data rates is to increase the signal to interference plus noise ratio (SINR); the antenna system can significantly improve SINR by increasing directivity. Directivity can be improved by arraying multiple antennas together to form an array. This arraying of antennas increases the effective aperture of the antenna resulting in a more directional beam. The directional antenna radiation pattern or beam can be utilized to direct the signal to the desired direction of communication, or conversely point the antenna radiation pattern in the direction for desired reception. As the antenna radiation pattern narrows, increased transmission and reception in the direction of the main beam is realized, while decreased transmission and reception in other directions is reduced. A resulting improvement in SINR from this narrowing of the antenna beam is realized.
An additional benefit from arraying antenna elements together is the ability to change radiation pattern shape of the array by changing the number of antennas that are combined, or by introducing amplitude and or phase shifts in the feed lines used to connect and combine the various antenna elements together. Changing the radiation pattern of the antenna system during communications provides the ability to improve the communication link quality by optimizing the array pattern; this optimization can take the form of fine tuning the direction of the maxima of the radiation pattern, or can be implemented by increasing the number of antennas connected to increase the directivity of the antenna system. An additional benefit from modifying the radiation pattern can be realized by forming a null in the array pattern and then steering the null in the direction of an interfering source. This will result in improved SINR.
Recent developments in the art have provided for steering of antenna radiation characteristics as is described in commonly owned U.S. Pat. No. 7,911,402 titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION”, and issued Mar. 22, 2011; the contents of which are hereby incorporated by reference.
More recently, “beam steering antennas” have evolved toward applications for correcting situations where a wireless device may enter a location having little to no signal reception, otherwise known in the art as a “null” or “null field”. When the device enters a null, the beam steering mechanism activates to steer antenna radiation characteristics into a useable state or mode. More specifically, these Modal antennas are adapted with two or more modes of operation, wherein each mode exhibits unique radiation characteristics across the uniform antenna structure.